Physicists Ana Claudia Barbosa Aguiar and Peter Read of the University of Oxford in the United Kingdom wanted to see if they could recreate the hexagon in the lab. They placed a 30-liter cylinder of water on a slowly spinning table; the water represented Saturn’s atmosphere spinning with the planet’s rotation. Inside this tank, they placed a small ring that whirled more rapidly than the cylinder. This created a miniature artificial "jet stream" that the researchers tracked with a green dye.

(…)

“Most planetary scientists are not aware of how ubiquitous these sorts of patterns are in fluid dynamics.”- Saturn's Strange Hexagon Recreated in the Lab: Science

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat. We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate. The slight asymmetry induces a tendency for mode-locking between the plate and the polygon, where the polygon rotates by one corner for each complete rotation of the plate. – Polygons on a Rotating Fluid Surface Thomas R. N. Jansson et al

All of which begs the question: How does one get hexagonal-like craters on dry rocky bodies? Do dust particles 'electro-statically' adopt the fluid-like jet stream flow patterns?

"Our laws of force tend to be applied in the Newtonian sense in that for every action there is an equal reaction, and yet, in the real world, where many-body gravitational effects or electrodynamic actions prevail, we do not have every action paired with an equal reaction." — Harold Aspden

Physicists Ana Claudia Barbosa Aguiar and Peter Read of the University of Oxford in the United Kingdom wanted to see if they could recreate the hexagon in the lab. They placed a 30-liter cylinder of water on a slowly spinning table; the water represented Saturn’s atmosphere spinning with the planet’s rotation. Inside this tank, they placed a small ring that whirled more rapidly than the cylinder. This created a miniature artificial "jet stream" that the researchers tracked with a green dye.

(…)

“Most planetary scientists are not aware of how ubiquitous these sorts of patterns are in fluid dynamics.”- Saturn's Strange Hexagon Recreated in the Lab: Science

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat. We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate. The slight asymmetry induces a tendency for mode-locking between the plate and the polygon, where the polygon rotates by one corner for each complete rotation of the plate. – Polygons on a Rotating Fluid Surface Thomas R. N. Jansson et al

All of which begs the question: How does one get hexagonal-like craters on dry rocky bodies? Do dust particles 'electro-statically' adopt the fluid-like jet stream flow patterns?

Fluid dynamics is a result not a cause.

The cause is incoming charge (ie photons and ions/electrons), the Birkeland current.

Because charge (ie photons) has chirality, left and right spins, these spins oppose and thus sheets are created of different spin, this sets up the cylinders sheets that spin in opposite directions and that causes the diocotron instabilities in the fluids and thus a shape forms, round, hexagon, square...

Hexagons and other polygons can sometimes occur in hurricanes, so astrophysicists believe that fluid dynamics can explain what they call a “mysterious” phenomenon. In 2010 physicists from Oxford University spun a 30-liter cylinder of water, with a ring of viscous green dye inside spinning faster than the cylinder. Their thinking was that a “jet stream” analogue could provide a plausible description of what is happening on Saturn if several factors are ignored.

First, they did not produce concentric rings around the hexagon, each with different temperatures. Second, Saturn’s poles are hotter than theories predict. Third, there are aurorae at the poles. Fourth, there is electric charge flow connecting Saturn’s poles to its family of moons. Additionally, the winds in the polar vortex are four times faster than any hurricane, nor does it move around. Such kinetic experiments are insufficient in scope, since electrical effects are not considered. Perhaps the kinetic model should be stood on its head: the polygons in hurricanes should be reevaluated in the light of electrical theories.

Cassini managed to take a final monochrome image hours before splashdown?I thought hours would have been enough time to take a few more photographs.Maybe even a last photo or two after entering the atmosphere?

I read on, to see why that was the last image, when the descent still had hours to go.No explanation.As if we should consider it normal that they switched the cameras off hours early.

But I cannot believe they did.That is just the final image that they are giving us.

Then, they also show us this.

A natural color view, created using images taken with red, green and blue spectral filters, of the last image taken by the imaging cameras on NASA's Cassini spacecraft.

They take color filtered images of the monochrome image, to create a natural color view?

The instrument, a so-called Langmuir proble, was developed at the Swedish Institute of Space Physics in Uppsala. The upper atmosphere of Saturn is charged and consists primarily of hydrogen and hydrogen ions. The Langmuir probe can be compared with a weather station for electrically charged gas; it measures its density, temperature and velocity. It also measures particles’ energy and moreover gives a rough estimate of what the gas consists of.

”The first results are surprising,” says Jan-Erik Wahlund, IRF, principle investigator and responsible for the Langmuir probe on Cassini.Strong variations in density indicate that the electrically charged part of Saturn’s atmosphere (the so-called ionosphere) has a strong coupling to the visible rings that consist primarily of ice particles. The ice particles are also electrically charged.

”It is as though the small ice particles in the D-ring suck up electrons from the ionosphere,” says Jan-Erik Wahlund. ”As a result of the coupling, electrical flows of gas to and from the rings along the magnetic field of Saturn cause the greatest variations in density.”

The instrument, a so-called Langmuir proble, was developed at the Swedish Institute of Space Physics in Uppsala. The upper atmosphere of Saturn is charged and consists primarily of hydrogen and hydrogen ions. The Langmuir probe can be compared with a weather station for electrically charged gas; it measures its density, temperature and velocity. It also measures particles’ energy and moreover gives a rough estimate of what the gas consists of.

”The first results are surprising,” says Jan-Erik Wahlund, IRF, principle investigator and responsible for the Langmuir probe on Cassini.Strong variations in density indicate that the electrically charged part of Saturn’s atmosphere (the so-called ionosphere) has a strong coupling to the visible rings that consist primarily of ice particles. The ice particles are also electrically charged.

”It is as though the small ice particles in the D-ring suck up electrons from the ionosphere,” says Jan-Erik Wahlund. ”As a result of the coupling, electrical flows of gas to and from the rings along the magnetic field of Saturn cause the greatest variations in density.”

According to a new paper from Imperial College , Saturn's magnetic field is refusing to confirm to existing thinking.

The findings, which appear in a Cassini end-of-mission results article in Science, show that Saturn's magnetic field has a tilt of less than 0.01 of a degree.

Scientists had previously thought that a planet could only form a magnetic field if there is discernible tilt. Earth's, for example, is 11 degrees.

Professor Michele Dougherty explained that measuring the tilt itself is also challenging. "Each time we more accurately measure the tilt of Saturn's magnetic field, it gets smaller, until now we are in a position where it is smaller than a hundredth of a degree."

The tilt is important because it sustains currents in the liquid metal layer deep within the planet. On Sarth the liquid is iron-nickel surrounding the solid iron core.

Saturn's core is thought to consist of a metallic hydrogen layer around it's small, rocky core.

There's a possibility that the atmosphere on the planet is obstructing Imperial's magnetometer which was onboard the Cassini probe. However scientists still think this might change how they look at magnetic fields.

Saturn might also have more than one way of generating magnetic fields, with a deeper layer made up of liquid hydrogen producing small, stable fields.

Even weirder is the discovery that an electrical current flows from the D ring of Saturn to the planet's surface.

Despite burning up in Saturn's atmosphere in September 2017 the mission is still yielding interesting data.

The Imperial team is also considering combining results from the magnetometer with gravity data to build a more accurate picture of the size, mass and density of Saturn's core.

While it's unusual to hear scientists describe things as weird, but Saturn's mysteries do often give experts some real head scratchers.

"...One goal was to probe the roots of the powerful winds that whip clouds on the gas giants into distinct horizontal bands. Scientists assumed the winds would either be shallow, like winds on Earth, or very deep, penetrating tens of thousands of kilometers into the planets, where extreme pressure is expected to rip the electrons from hydrogen, turning it into a metallike conductor. The results for Jupiter were a puzzle: The 500-kilometer-per-hour winds aren't shallow, but they reach just 3000 kilometers into the planet, some 4% of its radius. Saturn then delivered a different mystery: Despite its smaller volume, its surface winds, which top out at 1800 kilometers per hour, go three times deeper, to at least 9000 kilometers. “Everybody was caught by surprise,” Iess says.

"Scientists think the explanation for both findings lies in the planets' deep magnetic fields. At pressures of about 100,000 times that of Earth's atmosphere—well short of those that create metallic hydrogen—hydrogen partially ionizes, turning it into a semiconductor. That allows the magnetic field to control the movement of the material, preventing it from crossing the field lines. “The magnetic field freezes the flow,” and the planet becomes rigid, says Yohai Kaspi, a planetary scientist at the Weizmann Institute of Science in Rehovot, Israel, who worked with Iess. Jupiter has three times Saturn's mass, which causes a far more rapid increase in atmospheric pressure—about three times faster. “It's basically the same result,” says Kaspi, but the rigidity sets in at a shallower depth.

"The Juno and Cassini data yield only faint clues about greater depths. Scientists once believed the gas giants formed much like Earth, building up a rocky core before vacuuming gas from the protoplanetary disc. Such a stately process would have likely led to distinct layers, including a discrete core enriched in heavier elements. But Juno's measurements, interpreted through models, suggested Jupiter's core has only a fuzzy boundary, its heavy elements tapering off for up to half its radius. This suggests that rather than forming a rocky core and then adding gas, Jupiter might have taken shape from vaporized rock and gas right from the start, says Nadine Nettelmann, a planetary scientist at the University of Rostock in Germany.

"The picture is still murkier for Saturn. Cassini data hint that its core could have a mass of some 15 to 18 times that of Earth, with a higher concentration of heavy elements than Jupiter's, which could suggest a clearer boundary. But that interpretation is tentative, says David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena and a coinvestigator on Juno. What's more, Cassini was tugged by something deep within Saturn that could not be explained by the winds, Iess says. “We call it the dark side of Saturn's gravity.” Whatever is causing this tug, Stevenson adds, it's not found on Jupiter. “It is a major result. I don't think we understand it yet.”

"Because Cassini's mission ended with the Grand Finale, which culminated with the probe's destruction in Saturn's atmosphere, “There's not going to be a better measurement anytime soon,” says Chris Mankovich, a planetary scientist at the University of California, Santa Cruz. But although the rings complicated the gravity measurements, they also offer an opportunity. For some unknown reason—perhaps its winds, perhaps the pull of its many moons—Saturn vibrates. The gravitational influence of those oscillations minutely warps the shape of its rings into a pattern like the spiraling arms of a galaxy. The result is a visible record of the vibrations, like the trace on a seismograph, which scientists can decipher to plumb the planet. Mankovich says it's clear that some of these vibrations reach the deep interior, and he has already used “ring seismology” to estimate how fast Saturn's interior rotates.

"Cassini's last gift may be to show how fortunate scientists are to have the rings as probes. Data from the spacecraft's final orbits enabled Iess's team to show the rings are low in mass, which means they must be young, as little as 10 million years old—otherwise, encroaching interplanetary soot would have darkened them (Science, 22 December 2017, p. 1513). They continue to rain material onto Saturn, the Cassini team has found, which could one day lead to their demise. But for now they stand brilliant against the gas giant, with more stories to tell."